Polypeptides possessing a nitrilase activity and method of converting nitriles to carboxylates by means of said polypeptides

ABSTRACT

The present invention relates to novel polypeptides having a nitrilase activity and to the genetic tools for producing them, namely: 
     the DNA sequence coding for a polypeptide having a nitrilase activity and capable of hydrolyzing nitriles to carboxylates, 
     an analog of this sequence resulting from the degeneracy of the genetic code, 
     a DNA sequence hybridizing with one of these sequences or a fragment thereof and coding for a polypeptide having a nitrilase activity, 
     expression cassettes and microorganisms enabling them to be obtained. 
     Application: enzymatic conversion of nitriles to carboxylates.

This application is a divisional of U.S. patent application Ser. No. 08/194,588, filed Feb. 10, 1994, now abandoned, which is a continuation-in-part of U.S. patent application Ser. No. 08/102,747, filed Aug. 6, 1993, now abandoned.

The present invention relates to novel polypeptides having a nitrilase activity and to the genetic engineering tools for producing them, namely a DNA sequence, the expression cassettes carrying this recombinant DNA sequence, and the recombinant microorganisms (host microorganisms) containing said DNA sequence.

The present invention further relates to an enzymatic method of converting nitriles to carboxylates by means of the polypeptides according to the invention or a host microorganism containing the DNA sequence according to the invention.

A first particular application of the method of the invention is the enzymatic synthesis of ammonium adipate or ammonium 5-cyanovalerate by the hydrolysis of adiponitrile with the aid of a polypeptide or host microorganism according to the invention.

Ammonium adipate is known to be a particularly valuable product because it can be converted to adipic acid, a product which is itself widely used for the preparation of nylon 6,6.

The enzymatic hydrolysis of dinitriles has been described by numerous authors. However, the routes by which these dinitriles are hydrolyzed to organic acids are not often referred to. The theoretical hydrolysis scheme is as follows: ##STR1## NH=nitrile hydratase Ni=nitrilase

A=amidase

R=(CH₂)_(n), n being an integer equal to 4 in the case of adiponitrile.

In actual fact, it is very often observed that certain routes are preferred and that certain products are not formed or else are not hydrolyzed.

Among the microorganisms for which it has been possible to demonstrate the existence of an enzymatic activity permitting this hydrolysis, there may be mentioned in particular the strains belonging to the genus Fusarium, which degrade succinonitrile and adiponitrile, although the reaction products are not indicated [Goldlust et al., Biotechnol. and Appl. Biochem., 1989, 11, 581]; the strains belonging to the genus Pseudomonas, which degrade adiponitrile [Yanase et al., Agric. Biol. Chem., 1982, 46, 2925]; and the strains belonging to the genus Rhodococcus, in particular Rhodococcus rhodochrous NCIB 11 216, which hydrolyzes adiponitrile to adipic acid [Bengis-Garber et al., Appl. Microbiol. Biotechnol., 1989, 32, II], and also Rhodococcus rhodochrous K22, whose nitrilase permits the hydrolysis of adiponitrile and glutaronitrile [Yamada et al., J. Bacteriol., 1990, 172 (9), 4807-4815], albeit with a low activity ratio compared with that for the hydrolysis of aromatic nitriles.

Consequently, it can be seen that the enzymatic hydrolysis of dinitriles is rather complex: in all cases, although the first CN group is hydrolyzed by the enzyme, the second group is not hydrolyzed at all in some cases, or else is hydrolyzed at a very low rate in other cases.

It has now been found that it is possible to hydrolyze nitriles to carboxylates, and more particularly dinitriles to carboxylates or dicarboxylates, totally and rapidly, by using appropriately selected enzymes either as such or, preferably, in the form of recombinant microorganisms which generate them.

A second particular application of the invention is the enzymatic synthesis of ammonium methioninate: ##STR2## from methiononitrile: ##STR3##

Methionine is one of the only aminoacids which is currently produced on a large industrial scale. It constitutes a sulphurized nutriment which is useful, as a growth factor, in feeding animals.

One of its main synthesis chemical routes is the hydrolysis of methionitrile to ammonium methioninate, using a strong acid. One major drawback of this chemical hydrolysis is that it generates a very high coproduction of salts which are difficult to recycle and which are detrimental to the environment.

The Applicant takes credit for having demonstrated an advantageous enzymatic alternative to the chemical hydrolysis, said alternative solving the problem of detrimental coproduction of salts.

The present invention therefore relates to novel polypeptides having a nitrilase activity which have been isolated from a strain of Comamonas testosteroni. More precisely, these polypeptides are prepared by extraction and purification from cultures of natural or recombinant microorganisms, the purification being effected by a series of steps consisting in preparing an enzymatic extract from the cell culture, precipitating this extract with ammonium sulfate and purifying it by different steps involving chromatography and gel filtration. These steps, which employ techniques well known to those skilled in the art, are described in detail in the illustrative Examples below.

In the present description, "nitrilase activity" denotes the direct conversion of a nitrile to an ammonium carboxylate, the corresponding amide not being a substrate for the enzyme.

The invention further relates to a DNA sequence coding for a polypeptide having a nitrilase activity. The DNA sequence coding for a polypeptide of the invention can be selected from:

the DNA sequence coding for a polypeptide having a nitrilase activity, as shown in FIG. 4 and designated by SEQ ID NO: 4: in the enclosed sequence listing,

an analog of this sequence resulting from the degeneracy of the genetic code,

or else a DNA sequence hybridizing with one of these sequences or with a fragment thereof and coding for a polypeptide having a nitrilase activity.

Such a DNA sequence can be obtained by cloning the genomic DNA fragment coding for the desired polypeptide, with the aid of nucleotide probes produced from the purified polypeptide.

The invention further relates to the expression cassettes which carry the above-defined recombinant DNA sequence together with the signals ensuring its expression. These expression cassettes can either be integrated in the genome of the host or located on an expression vector such as a plasmid containing a selection means.

In particular, these expression cassettes contain transcription and translation initiation regions which contain a ribosome binding site and a promoter sequence. These regions may be homologous or heterologous with the microorganism which naturally produces the polypeptide.

The choice of these regions depends especially on the host used. In particular, when the host microorganisms are procaryotic, the heterologous promoter can be selected from strong bacterial promoters such as the tryptophan operon promoter Ptrp of E. coli, the lactose operon promoter Plac of E. coli, the phage lambda right promoter P_(R), the phage lambda left promoter P_(L), the strong promoters of Pseudomonas and Comamonas and the strong promoters of Corynebacteria.

More particularly, in the case of the phage lambda right promoter, the thermosensitive form P_(R) Cits may be preferred. In the case of eucaryotic microorganisms such as yeasts, the promoters can originate from glycolytic yeast genes such as the genes coding for phosphoglycerate kinase (PGK), glyceraldehyde-3-phosphate dehydrogenase (GPD), lactase (LAC4) and enolase (ENO).

As far as the ribosome binding sites are concerned, the one derived from the lambda CII gene, as well as those derived from homologous genes of Comamonas or Pseudomonas or those derived from genes of Corynebacteria, are used preferentially when the host microorganism is procaryotic.

A region permitting a termination of the translation and functional transcription of the envisaged host can be positioned at the 3' end of the coding sequence. The expression cassette also comprises one or more markers making it possible to select the recombinant host. The preferred markers are dominant markers, i.e. those conferring a resistance to antibiotics such as ampicillin or streptomycin, or to other toxic products.

Enterobacteria such as E. coli, bacteria belonging to the genera Comamonas or Pseudomonas, and corynebacteria such as those belonging to the genera Corynebacterium, Brevibacterium or Rhodococcus, may be mentioned in particular among the host microorganisms used.

The invention further relates to the microorganisms containing the recombinant DNA sequence according to the invention, for example on a plasmid containing a selection means.

A recombinant microorganism containing said DNA sequence on a plasmid structure was deposited in the Collection Nationale de Cultures de Micro-organismes (C.N.C.M.) (Institut Pasteur, 25 rue du Docteur Roux, Paris) under no. I-1242 on 21st Jul. 1992. This microorganism is the strain E. coli TG1, which contains plasmid pXL2148; this microorganism is also identified by the Applicant using the reference G4207.

The invention further relates to the microorganisms capable of converting nitriles to carboxylates, and more particularly aliphatic dinitriles of the formula NC--R--CN, in which R is a linear or branched alkylene group having from 1 to 10 carbon atoms, to carboxylates, or else aliphatic sulphurized mononitriles such as methiononitriles.

Beyond acquiring their structures I and II during their synthesis by the microorganisms according to the invention, it is important that the polypeptides in question stabilize in their structures III and IV so as to possess an optimal nitrilase activity.

The Applicant takes credit for having discovered means for favoring the above-mentioned stabilization.

Thus any microorganism according to the invention preferably contains:

at least one protein agent for assisting the folding of the polypeptides which the microorganism synthesizes, and in particular the nitrilase referred to in the present disclosure,

and/or the genes coding for such an agent, this agent being present in a greater amount than that corresponding to the base level of the microorganism in question.

In terms of the present invention, base level is understood as meaning the maximum level which can be attained by the corresponding wild-type microorganism in question.

Advantageously, this agent is the GroE chaperone of E. coli or its homolog of eucaryotic or procaryotic origin.

The GroE chaperone of E. coli is normally present in the wild-type strains.

The genes coding for the agent are carried by the chromosome or by an extrachromosomal element (plasmid, phage). They are preferably amplified by any known and appropriate means so as to favor the synthesis of the agent in the microorganism.

The genes coding for the agent are under the dependence of expression systems homologous or heterologous with their host microorganism.

The invention further relates to the method of converting nitriles to carboxylates with the aid of a polypeptide according to the invention or a recombinant microorganism which generates it. This method consists in bringing the nitrile to be converted into contact with a polypeptide or recombinant microorganism as defined above. The process is generally carried out at room temperature. In one particular embodiment of the invention, the polypeptide or recombinant microorganism is immobilized on or in a solid support.

The method of the invention is suitable for the conversion of nitriles to carboxylates and more particularly for the conversion to carboxylates, on the one hand, of dinitriles of the formula NC--R--CN, in which R is a linear or branched alkylene group containing 1 to 10 carbon atoms, to carboxylates, and on the other hand, of mononitriles, preferably aliphatic sulphurized mononitriles.

The method of the invention is particularly appropriate for the enzymatic synthesis of ammonium adipate from adiponitrile and ammonium methionate from methiononitrile.

The production of adipate determines a field of application of the invention in the synthesis of polyamides (NYLON®), whereas the production of methionate particularly belongs to the field of application of animal feed.

The Examples which follow afford an illustration of the characteristics and advantages of the present invention without however limiting its scope.

DESCRIPTION OF THE FIGURES

FIG. 1 shows the yield (%) of the hydrolysis of adiponitrile to cyanovalerate (curve a) and to ammonium adipate (curve b) as a function of the reaction time in hours for the strain Comamonas testosteroni sp.

FIGS. 2a and 2b show the restriction maps of plasmids pXL2075 and pXL2076.

FIG. 3 shows the restriction map of the SstI--SstI fragment of 4.1 kb containing the DNA sequence (called "nitrilase gene" in the Figure) coding for the polypeptide having the nitrilase activity according to the invention, said fragment being present in plasmids pXL2075 and pXL2076. The strategy for producing the XbaI-SstI fragment containing the DNA sequence according to the invention is also shown in this Figure.

FIG. 4 shows the DNA sequence SEQ ID NO: 4: according to the invention with its deduced amino acid sequence.

FIG. 5 shows the restriction map of plasmid pXL2087.

FIG. 6 shows the restriction map of plasmid pXL2148.

FIG. 7 shows the SDS-PAGE, 10% SDS, indicating the expression of the DNA sequence according to the invention in the strain E. coli TG1/pXL2027. Each lane corresponds to an amount of protein equivalent to 60 μl of culture at an optical density of 3 at 610 nm.

FIG. 8 shows the restriction map of plasmid pXL2158.

FIG. 9 shows the SDS-PAGE, 12.5% SDS, indicating the expression of the DNA sequence according to the invention in the strains TG1/pXL2158 and TG1/pXL2158+pXL2035 (GroE).

FIG. 10 shows the restriction map of plasmid pXL2169.

FIG. 11 shows the SDS-PAGE, 10% SDS, indicating the expression of the DNA sequence according to the invention in the strain Pseudomonas putida G2081-pXL2169.

The abbreviations used in the remainder of the description have the following meanings:

SSC: buffer commonly used for hybridizations, containing sodium citrate and NaCl (20×SSC=3M NaCl, 0.3M sodium citrate, pH 7)

SDS: sodium dodecylsulfate

FPLC: fast protein liquid chromatography

SDS-PAGE: gel electrophoresis based on sodium dodecylsulfate/polyacrylamide

IPTG: isopropyl β-D-thiogalactopyranoside

EXAMPLES Example 1 Purification of the Nitrilase of Comamonas Testosteroni Sp.

1-Preparation of the Cells

A strain of Comamonas testosteroni sp. was cultivated in a shake flask, at 28° C., for 15 h 30 min, in medium A having the following composition:

Medium A

    ______________________________________                                         Glucose         5            g/l                                               (NH.sub.4).sub.2 SO.sub.4                                                                      1            g/l                                               Na.sub.2 HPO.sub.4                                                                             5.24         g/l                                               KHPO.sub.4      2.77         g/l                                               Yeast extract   5            g/l                                               Casamino acids  1            g/l                                               ______________________________________                                    

This preculture was used to inoculate a 20 l fermenter containing 15 l of medium A. The pH, temperature, air flow rate and shaking speed were set to 6.6, 28° C., 300 l/h and 350 rpm respectively. After 24 h, 84 g of wet cells were harvested. This corresponds to a content by dry weight of cells of 0.9 g/l and to an optical density at 660 nm (OD_(660nm)) of 2.

2-Determination of the Enzymatic Activity on Adiponitrile

A cellular residue containing 13.1 mg of dry weight of cells was suspended in 2 ml of a 52.3 mM solution of adiponitrile in 50 mM potassium phosphate buffer, pH 7. The reaction was carried out at 25° C., with shaking, and the kinetics were followed by sampling. 5-Cyanovaleramide, adipamide, 5-cyanovalerate, adipamate and adipate were determined on each sample by high performance liquid chromatography (HPLC). The results are collated in FIG. 1, which shows the curves of the yield (on the ordinate) of cyanovalerate (curve a) and ammonium adipate (curve b). The respective rates of formation of cyanovalerate and adipate were greater than 0.45 and equal to 0.15 U/mg of dry weight of cells (1 U is equal to 1 μmol of product formed per minute).

3-Purification

All the purification steps were carried out in 50 mM Tris/HCl buffer, pH 7.5, 1 mM dithioerythritol (DTE), unless indicated otherwise. At each step, the nitrilase activity of the fractions was determined at pH 7 and at 25° C. in 10 mM phosphate buffer in the presence of 10 mM adiponitrile. The protein concentration of the pools was determined by the Coomassie blue method (PIERCE Protein assay kit). The proteins were analyzed by SDS-PAGE (Phastsystem, PHARMACIA).

The procedures of each step are discussed below.

Step 1: Crude Extract

57 g of wet cells were taken up in 85 ml of buffer and treated with ultrasound for 30 min (VIBRACELL sonicator from Bioblock: probe 13 mm; power 7; 40% of the cycle active). The OD_(660nm) thus dropped from 97 to 60. After centrifugation at a maximum of 48,000 g for 60 min, the supernatant was recovered.

This supernatant was brought to 15% saturation by the gradual addition of ammonium sulfate. After 1 h, the suspension was centrifuged for 30 min at a maximum of 30,000 g. The supernatant was brought to 50% saturation. After 1 h, the suspension was centrifuged under the same conditions and the precipitate was recovered and then dialyzed against the buffer for two days.

Step 2: Ion Exchange Column (Q Sepharose Fast Flow)

The dialyzed fraction was loaded at a rate of 125 ml/h on to a column (26×380 mm) of "Q Sepharose Fast Flow" equilibrated with the buffer at a rate of 250 ml/h. The column was percolated at a rate of 250 ml/h by the following solutions in succession:

166 ml of buffer

180 ml of a gradient of 0 to 0.2M KCl in the buffer

180 ml of buffer to which 0.2M KCl had been added

270 ml of a gradient of 0.2 to 0.4M KCl in the buffer

180 ml of buffer to which 0.4M KCl had been added

200 ml of buffer to which 1M KCl had been added

The fraction having the nitrilase activity was eluted in a volume of 129 ml during the 0.2M KCl stage.

The following steps are carded out on the FPLC system (Pharmacia).

Step 3: Gel Filtration (FPLC Superdex 200)

The previously obtained fraction having the nitrilase activity (129 ml) was concentrated to 12 ml by precipitation of the proteins with ammonium sulfate at 80% saturation, followed by dialysis against the buffer. The fraction concentrated in this way (12 ml) was loaded in 2 batches on to the column of gel (16×600 mm) equilibrated with the buffer to which 0.1M KCl had been added, at a rate of 0.8 ml/min. The fractions having the nitrilase activity were eluted with the above buffer at a rate of 1 ml/min and in a total volume of 36 ml. These fractions correspond to a molecular weight of 280 kDa.

Step 4: Column of Hydroxyapatite (BIO-RAD HPHT; 7.8×100 mm)

The fractions obtained above were concentrated to 8 ml by ultrafiltration (DIAFLO PM39 membrane, AMICON). The concentrated solution was injected on to the column of hydroxyapatite equilibrated with the buffer to which 10 μM CaCl₂ had been added. The column was percolated at a rate of 0.5 ml/min with the following in succession:

5 ml of equilibration buffer

15 ml of a gradient of 0 to 350 mM potassium phosphate in the equilibration buffer

10 ml of the equilibration buffer to which 350 mM potassium phosphate had been added

The fractions having the nitrilase activity were eluted between 62 and 135 mM potassium phosphate in a volume of 3 ml.

Step 5: Hydrophobic Interaction Column (FPLC-Phenyl Superose HR 5/5)

The active fractions obtained above, brought to 15% saturation with ammonium sulfate, were loaded at a rate of 0.5 ml/min on to the column equilibrated with buffer containing ammonium sulfate at 15% saturation. The column was percolated with:

6 ml of equilibration buffer

12 ml of a decreasing ammonium sulfate gradient of 15% to 0% ammonium sulfate saturation in the buffer

23 ml of buffer

Some of the fractions having the nitrilase activity were eluted during the washing of the column with the equilibration buffer. These active fractions were reinjected under the same conditions. This operation was performed twice. The active fractions eluted after the gradient were pooled (volume 51 ml).

Step 6: Gel Filtration (FPLC-Superdex 200)

The 51 ml were concentrated to 3 ml by ultra-filtration on a membrane (DIAFLO PM30, AMICON). These 3 ml were loaded on to the column (16×600 mm) equilibrated with the buffer to which 0.1M KCl had been added. The 9 ml containing the activity were eluted at a position corresponding to a molecular weight of 280 kDa. This solution was brought to 36% with glycerol and then frozen for 15 days.

Step 7: Ion Exchange Column (FPLC Mono Q HR 5/5)

The protein solution was thawed and loaded on to the column equilibrated with the buffer containing 0.1M KCl, at a rate of 0.5 ml/min. The column was percolated with the following in succession:

15 ml at 0.5 ml/min of buffer to which 0.1M KCl had been added

4.5 ml at 1 ml/min of buffer to which 0.1M KCl had been added

15 ml at 1 ml/min of a gradient of 0.1 to 0.4M KCl in the buffer

10 ml of buffer to which 0.4M KCl had been added

The active fractions were eluted between 0.15 and 0.3M KCl. These fractions are homogeneous. SDS-PAGE analysis reveals two bands very close to 38 and 39 kDa. The fractions thus obtained will hereafter be called "purified nitrilase".

The data from each of the above purification steps are collated in Table 1 below:

                                      TABLE 1                                      __________________________________________________________________________     PURIFICATION OF THE NITRILASE OF Comamonas testosteroni sp.                                          ACTIVITY YIELD                                                         Vol.                                                                              Proteine                                                                            Total                                                                              Specific                                                                            Protein                                                                            Activity                                    PURIFICATION STEP                                                                            ml mg   U   U/mg %   %    PF                                     __________________________________________________________________________     0 - Crude Extract                                                                            61 920  62,000                                                                               68 100 100  1                                      2 - Q Sepharose FF                                                                           130                                                                               245  47,000                                                                               190                                                                               27  76   2.8                                    3 - Gel Filtration                                                                           36 27   56,000                                                                             2,100                                                                               2.9 90   30                                     4 - Hydroxyapatite Column                                                                    3  12   49,000                                                                             4,100                                                                               1.3 79   60                                     5 - Phenyl Superose                                                                          51 11   11,000                                                                             1,000                                                                               1.1 18   15                                     6 - Gel Filtration                                                                           9  2.7   6,300                                                                             2,300                                                                               0.3 10   34                                     7 - Mono Q HR 5/5                                                                            2.9                                                                               1     1,200                                                                             1,200                                                                               0.01                                                                                2   18                                     __________________________________________________________________________      ABBREVIATIONS: PF = purification factor; U = 1 μmol/h                 

4-Determination of the N-Terminal Sequence of the Nitrilase

Taking the purified protein, the N-terminal sequence of 27 amino acids was determined by Edman automatic sequential degradation using an "Applied Biosystems Model 470 A" apparatus. This sequence, designated by SEQ ID NO: 1: in the enclosed sequence listing, is as follows: ##STR4## A search of sequence libraries made it possible to find a 53% identity with the nitrilase of Klebsiella pneumoniae active on bromoxynil, which forms the subject of European patent application no. 373 173.

5-Activity of the Purified Nitrilase

a) Influence of the pH on the activity of the nitrilase:

The purified nitrilase was tested at different pH values on two substrates, adiponitrile and 5-cyanovalerate, under the conditions indicated in Table 2 below.

                  TABLE 2                                                          ______________________________________                                         ACTIVITY OF THE PURIFIED NITRILASE ON                                          ADIPONITRILE AND CYANOVALERATE AS A                                            FUNCTION OF THE pH                                                                      BUFFER      SPECIFIC ACTIVITY                                         SUBSTRATE  Nature     pH     U/mg of protein                                   ______________________________________                                         Adiponitrile                                                                              Acetate    3.0    2,300                                                        Acetate    4.0    2,900                                                        Acetate    4.5    2,800                                                        Acetate    5.0    2,700                                                        Phosphate  6.0    2,900                                                        Phosphate  7.0    2,700                                                        Phosphate  8.0    2,800                                             5-Cyanovalerate                                                                           Acetate    4.0      450                                                        Acetate    5.5      180                                                        Phosphate  7.0      30                                                         Phosphate  8.0       6                                              ______________________________________                                          COMMON CONDITIONS: [substrate] = 10 mM; buffer 10 mM; T 25° C.;         [nitrilase] = 12 μg/ml for cyanovalerate and 3 μg/ml for                 adiponitrile (fraction, step 6); U (adiponitrile) = μmol of                 cyanovalerate formed/h, U (cyanovalerate) = μmol of adipate formed/h. 

b) Activity range of the purified nitrilase:

The activities of the purified nitrilase were measured on adiponitrile, 5-cyanovaleramide, 5-cyanovaleric acid, benzonitrile, propionitrile and acrylonitrile. The results are given in Table 3.

                  TABLE 3                                                          ______________________________________                                         RELATIVE ACTIVITY OF THE PURIFIED NITRILASE                                    ON VARIOUS NITRILES                                                            SUBSTRATE     RELATIVE ACTIVITY (%)                                            ______________________________________                                         Adiponitrile  100                                                              5-Cyanovaleramide                                                                            28                                                               5-Cyanovaleric acid                                                                          22                                                               Acrylonitrile 23                                                               Propionitrile  6                                                               Benzonitrile   4                                                               ______________________________________                                          COMMON CONDITIONS: acetate buffer = 10 mM, pH 4; substrate = 10 mM; volum      = 3 ml; T = 25° C.; reaction time = 1 or 3 h; proteins: from 5 to       30 μg/ml.                                                             

Example b 2 Cloning of the Nitrilase of Comamonas testosteroni Sp.

A nucleotide probe was synthesized from the NH₂ -terminal sequence presented in Example 1; the high percentage of GC in the strains of Comamonas described in the literature (Tamaoka et al, Int. J. Syst. Bacteriol., 1987, 37, 52-59) dictated a choice for the third position of the codon in the case of lysines and in the case of valine. The probe is a 26 mer of degeneracy 128 (in the sequence of nucleotidic bases N replaces A, C, G or T): ##STR5##

The MKNYPTVKV amino acid sequence given above corresponds to the SEQ ID NO: 2: in the enclosed sequence listing.

The strategy followed consisted first of all in verifying the specificity of this nucleotide probe and determining the nature of the genomic DNA fragments to be cloned. Briefly, the genomic DNA of Comamonas testosteroni sp. was digested with several restriction enzymes (SstI, SphI, BamHI, PstI etc.) corresponding to sites usable for cloning.

After electrophoresis on agarose gel and transfer to a nylon membrane, the various digestions were hybridized with the probe. The probe is found to have a sufficient specificity under the hybridization conditions used (hybridization buffer=5×SSC, 5×Denhardt, 0.1% SDS, 50 mM Na₃ PO₄, pH 6.5, 250 μg/ml of ssDNA; hybridization temperature 50° C.; washing conditions: 1 h, 6×SSC, room temperature, and 5 min, 2×SSC, 0.1% SDS, 50° C.).

Under these conditions, the probe made it possible to obtain important signals without ambiguity, in particular in the case of digestions with SstI, SphI, BamHI and PstI. The hybridization blots show in particular the existence of a single SstI--SstI fragment of about 4 kb. To clone this fragment, the fragments of 3.5 to 4.5 kb from an SstI digestion of the genomic DNA were purified by preparative electrophoresis on agarose and electroelution and then ligated to plasmid pUC19 (YANISCH et al., Gene, 33 (1985) 103), itself digested with SstI. After transformation in the strain DH5α (Clontech Laboratory, Palo Alto, Calif.), 600 white clones on LB amp X-gal (SAMBROOK et al., Molecular Cloning, A Laboratory Manual, 2nd edition, Cold Spring Harbor Laboratory Press, Cold Spring Harbor Laboratory, N.Y., 1989) were subcultured individually, transferred to a nylon membrane and then analyzed by hybridization with the probe used to hybridize the Southern blot, under the same conditions of stringency. Six clones were thus identified as hybridizing very strongly with the probe. Two clones which had inserted the same fragment of about 4.1 kb in both orientations (pXL2075 [FIG. 2a] and pXL2076 [FIG. 2b]) were analyzed in greater detail (restriction mapping, partial sequencing using the probe as primer, and Southern blot). It was thus possible to show that the 5' part of the gene which hybridizes with the probe is located on an XhoI-XbaI fragment of about 150 bp orientated in the XhoI to XbaI direction. FIGS. 2a and 2b show the restriction maps of these plasmids.

Example 3 Sequence of a Fragment of 1194 bp Containing the DNA Coding for the Polypeptide Having the Nitrilase Activity

The location, on the cloned insert, of the fragment of 1194 bp containing the sequenced nitrilase gene is indicated in FIG. 3. The strategy for the sequencing of this fragment, performed by conventional methods known to those skilled in the art, is also indicated in FIG. 3. The various sequences were all obtained by the chain termination method (sequenase kit in the presence of 7-deaza-dGTP; (³⁵ S)dATP either on single-stranded matrices of recombinant M13 (mp 18 or 19, see YANISCH et al., op. cit.) carrying subfragments, or directly on plasmid pXL2075). Several specific primers were also synthesized for this purpose.

The DNA sequence SEQ ID NO: 4: according to the invention is shown in FIG. 4. The average G+C content of the sequence obtained is 45.7%, which is lower than the G+C content of 61.5% described for other strains of Comamonas (Tamaoka et al., op. cit.). An analysis of the sequence obtained made it possible to characterize an open reading frame of 1064 bp, hereafter called the nit gene, coding for a polypeptide of 354 residues corresponding to a molecular weight of 38,725 Da. The amino acid sequence of this polypeptide is indicated in SEQ ID NO: 4:, in SEQ ID NO: 5: and in FIG. 4. This polypeptide comprises the NH₂ -terminal sequence used to synthesize the probe, as well as three internal sequences determined on tryptic fragments of the purified nitrilase (these internal sequences are underlined in FIG. 4).

This open reading frame thus represents the DNA sequence according to the invention.

Example 4 Homology with Other Proteins, Identification of Homologous Sequence

The DNA sequence according to the invention was compared with all the sequences in the NBRF protein library; only one significant homology was found with the nitrilase of Klebsiella ozaenae specific for the herbicide Bromoxynil (Stalker et al., J. Biol. Chem., 1988, 263, 6310-6314). The two nitrilases exhibit a strict homology of 34.9% distributed over 320 amino acids. Furthermore, this protein exhibits a strict homology of 34.4%, distributed over 312 amino acids, with the nitrilase of Arabidopsis specific for indole-3-acetonitrile [Bartling et al., Eur. J. Biochem., 205, 417-424, 1992].

Example 5 Expression of the Nitrilase in E. coli

To confirm the identification of the coding frame with the purified nitrilase, the nit gene, preceded by its own ribosome binding site, was placed under the control of the lactose operon promoter of E. coli in accordance with the procedure described below: Plasmid pXL2087, described in FIG. 5, was obtained by insertion of the XhoI-NcoI fragment derived from plasmid pXL2075 between the corresponding sites of vector pMTL25 (Chambers et al., Gene, 1988, 68, 139-149). This plasmid therefore contains the lactose operon promoter Plac, followed by the ribosome binding site and the structural nitrilase gene, as well as a gene conferring ampicillin resistance. The expression of the nitrilase was visualized in the strain E. coli TG1 containing plasmid pXL2087. For this purpose, the strain TG1/pXL2087 and the control strain TG1/pUC19 were cultivated for 16 h at 37° C. in LB medium (Miller, J. H., 1972, Experiments in Molecular Genetics--Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.) containing 100 μg/ml of ampicillin, and then diluted 100-fold in the same medium and at the same temperature. When the cultures had reached an OD₆₁₀ of between 0.5 and 1, IPTG was added at a final concentration of 1 mM. After 2 h of culture, the bacteria were collected.

After sonication of the cells, the expression of the nitrilase was measured by SDS-PAGE in the crude fraction or, after centrifugation, in the residue and the supernatant. The results are presented in FIG. 7 and show a high level of expression of the nitrilase in the extracts of cells cultivated in the presence of IPTG; however, this protein is essentially in insoluble form.

In FIG. 7, M represents the molecular weight marker; the molecular weights are indicated in kDa. Also, the lanes have the following meanings:

    ______________________________________                                                         TG1 +              TG1 +                                                TG1 +  pUC19 →                                                                           TG1 +    pXL2087 +                                            pUC19  IPTG      pXL2087  IPTG                                        ______________________________________                                         Crude Fractions                                                                           A        D         G      J                                         Residues   B        E         H      K                                         Supernatants                                                                              C        F         I      L                                         ______________________________________                                    

Starting from plasmid pXL2087, plasmid pXL2148 was prepared by insertion of the XhoI-EcoRI fragment of plasmid pXL2087, carrying the gene coding for the nitrilase, between the Sa1I and EcoRI sites of pBR322 [SUTCLIFFE, Nucleic Acid Res., 5 (1978) 2721-2730].

This plasmid pXL2148, whose restriction map is shown in FIG. 6, was also used to transform the strain E. coli TG1 by the calcium chloride method. The microorganisms were selected on ampicillin. The strain E. coli TG1 (pXL2048) (G4207) transformed in this way was deposited in the Collection Nationale de Cultures de Micro-organismes in Paris (Institut Pasteur, 25 rue du Docteur Roux) under no. I-1242 on 21st Jul. 1992. Other expression systems were used to produce the nitrilase in a recombinant microorganism.

First of all, the nit gene was expressed in E. coli behind the tryptophan operon promoter of E. coli under the dependence of the RBS of the phage λ CII gene. To do this, an NdeI restriction site was created on the initiation codon of nit, and the NdeI/AhaII fragment of 117 bp, containing the 5' part of the nit gene, was amplified by the PCR technique starting from pXL2087. An NdeI/XbaI fragment of 61 bp, obtained after digestion of the first fragment, was ligated to the EcoRI/NdeI fragment containing the tryptophan operon promoter of E. coli and the ribosome binding site of the bacteriophage λ CII gene (Ptrp-RBSCII) between the EcoRI and XbaI sites of pUC19 (Yanisch et al., Gene, 33 (1985) 103) to give plasmid pXL2149. The EcoRI/XbaI fragment of pXL2149, containing the 5' part of nit behind Ptrp-RBSCII, was ligated to the XbaI/Sa1I fragment of pXL2087 containing the 3' part of the nit gene between the EcoRI and Sa1I sites of pXL642 (Mayaux, unpublished results): pXL642 is a derivative of pXL534 (Latta et al., 1990, DNA Cell Biol., 9, 129) in which the superexpressed gene codes for a tissue inhibitor of metalloproteases and in which the HindIII site downstream from the superexpressed gene has been replaced by the EcoRI/HindIII multisite of M13mp18.

The final plasmid pXL2158 is therefore a derivative of pBR322 (Sutcliffe, Nucleic Acid Res., 5 (1978) 2721) containing a gene conferring ampicillin resistance and the nit gene under the control of Ptrp-RBSCII. The restriction map of this plasmid pXL2158 is shown in FIG. 8.

Plasmid pXL2158 was used to transform the strain E. coli TG1. The strain TG1/pXL2158 and the control strain TG1 containing vector pMTL22 were cultivated for 16 h at 30° C. in M9 glucose medium (Miller, J. H., 1972, Experiments in Molecular Genetics, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y.) containing 100 μg/ml of ampicillin and 100 μg/ml of tryptophan. These cultures were diluted 100-fold in the same medium, but without tryptophan, and cultivated for 6 hours at the same temperature. After sonication of the cells, the expression of the nitrilase of Comamonas testosteroni NI 1 was measured in 12.5% SDS-PAGE in the crude fraction or, after centrifugation, in the residue and in the supernatant. The results are shown in FIG. 9.

    ______________________________________                                                TG1/                                                                           pXL2158 +                                                                      pXL2035  TG1/pXL2158 TG1 + pMTL22                                       ______________________________________                                         Supernatant                                                                             A          D           G                                              Residue  B          E           H                                              Total Extract                                                                           C          F           I                                              ______________________________________                                    

This gel shows that pXL2158 induces a strong expression of the nitrilase, predominantly in insoluble form.

The efficacy of the GroE chaperone was then tested (Hemmingsen et al., 1988, Nature, 333, 330) in order to assist the correct folding of the nitrilase. For this purpose, plasmid pXL2035 was constructed in the following manner. The EcoRI/HindIII fragment of 2.2 kb, containing the groES and groEL genes coding for the two subunits of GroE, was extracted from plasmid pOF39 (Fayet et al., 1986, Mol. Gen. Genet., 202, 435) and introduced between the EcoRI and HindIII sites of vector pDSK519 (Keen et al., 1988, Gene, 70, 191).

Plasmid pXL2035 was introduced into the strain TG1 containing pXL2158. The resulting strain was cultivated under the same conditions as before, in the presence of 50 mg/l of kanamycin; the expression results are visualized in FIG. 9. It is found that the superexpression of GroE (only the GroEL subunit is visible on the gel) solubilizes the bulk of the nitrilase expressed from pXL2158.

The same expression system was used to produce the nitrilase in Pseudomonas putida. Thus, starting from pXL2158, the NdeI/NcoI fragment of 1256 bp and the NcoI/BamHI fragment of 535 bp were introduced between the NdeI and BamHI sites of pXL1841. pXL1841 (Blanche et al., 1991, J. Bacteriol., 173, 4637) is a derivative of pKT230 (Bagdasarian et al., 1981, Gene, 15, 237) expressing a Methanobacterium ivanovli gene behind Ptrp-RBSCII.

The final plasmid pXL2169 is therefore a derivative of pKT230 containing a gene conferring kanamycin resistance and the nit gene under the control of Ptrp-RBSCII (see FIG. 10). This plasmid was introduced into the strain Pseudomonas putida G2081. G2081 is a derivative of Pseudomonas putida KT2440 (Bagdasarian and Timmis, 1981, in Hofschneid and Goebel, Topics in Microbiology and Immunology, 47, Springer Verlag, Berlin) rendered resistant to nalidixic acid and rifampicin. Vector pDSK519 (Keen et al., 1988, Gene, 70, 191) was used as the control plasmid. G2081 (pXL2169) and the strain G2081 (pDSK519) were cultivated overnight at 30° C. in LB medium containing 20 mg/l of kanamycin. These precultures were diluted 100-fold in the same medium. The cultures were then continued for 7 h 30 min at the same temperature.

After sonication of the cells, the expression of the nitrilase of Comamonas testosteroni NI 1 was measured in 10% SDS-PAGE in the crude fraction or, after centrifugation, in the residue and in the supernatant. The results are presented in FIG. 11. Only the crude extract of the strain G2081 (pDSK519) was deposited (well D). For the strain G2081 (pXL2169), the total extract, the sonication residue and the sonication supernatant were deposited in wells C, B and A respectively. This experiment shows that the strain of Pseudomonas putida expresses large amounts of nitrilase in soluble form.

Example 6 Assay of the Nitrilase Activity of Recombinant Strains

The Examples which follow illustrate the nitrilase activity of the recombinant strains E. coli TG1 and Pseudomonas putida G2081.

The different plasmids integrated into these strains are as follows:

    ______________________________________                                         PLASMIDS CHARACTERISTICS                                                       ______________________________________                                         pXL2087  Recombinant plasmid which carries the                                          Comamonas NI 1 nitrilase gene under the control                                of the promoter P.sub.lac.                                            pXL2158  Recombinant plasmid which carries the                                          Comamonas NI 1 nitrilase gene under the control                                of the tryptophan promoter.                                           pXL2035  Recombinant plasmid which carries the genes                                    coding for GroE and S.                                                pXL2169  Broad host range plasmid with an insertion,                                    carrying the Comamonas NI 1 nitrilase gene under                               the control of P.sub.trp.                                             pDSK519  Control plasmid (see Example 5).                                      ______________________________________                                    

The activities of these strains, induced or non-induced, are measured on adiponitrile and 5-cyanovalerate at different pH values and are compared with the negative control strains: E. coli TG1, E. coli TG1 (pXL2035) and Pseudomonas putida G2081.

6.1-Preparation of the Cells

The cultures are carried out under the conditions described in Table 4. During the exponential growth phase, one of the two cultures of the recombinant strain is induced with 1 mM IPTG; after 2 h at 37° C., this culture is treated.

                  TABLE 4                                                          ______________________________________                                         CULTURE OF THE STRAINS                                                         MICROORGANISMS MEDIUM    OD.sub.660nm                                                                             DW (g/l)                                    ______________________________________                                         1 - E. coli TG1                                                                               a         3.1       0.90                                        2 - E. coli (pXL2087)                                                                         b         3.2       0.90                                        3 - E. coli (pXL2087)                                                                         c         2.5       0.90                                        4 - E. coli (pXL2035)                                                                         d         2.1       0.90                                        5 - E. coli (pXL2158)                                                                         b         3.1       0.80                                        6 - E. coli (pXL2035, 2158)                                                                   e         4.2       1.30                                        7 - P. putida (pXL1289)                                                                       d         2.1       0.98                                        8 - P. putida (pXL2169)                                                                       d         2.3       0.98                                        ______________________________________                                          ABBREVIATIONS: a = LB medium; b = LB medium + 100 μg/ml of Amp; c =         medium b + addition of 1 mM IPTG to OD.sub.660nm = 1; d = LB medium + 50       mg/l of kanamycin; e = M9 medium + 100 mg/l of ampicillin + 50 mg/l of         kanamycin; DW = dry weight.                                                    COMMON CONDITIONS:                                                             1 to 3: Inoculation in a ratio of 1/100 with a 16hour-old preculture;          culture time 5.75 h; T 37° C.                                           4 to 8: Inoculation in a ratio of 1/100 with a 17hour-old preculture at        37° C. with the addition of tryptophan; culture time in 15 l            fermenter: 23 h for E. coli and 7.5 h for P. putida; T 30° C.     

6.2-Specific Activity Measurements

The conditions of the specific activity measurements and the results are collated in Table 5.

                                      TABLE 5                                      __________________________________________________________________________     DETERMINATION OF THE ACTIVITIES OF THE                                         CONTROL STRAINS FOR THE RECOMBINANT STRAINS                                                   OPERATING CONDITIONS                                            MICROORGANISM       [DW] Volume                                                                              Activity                                         Nature  IPTG                                                                               State                                                                             Substrate                                                                           (g/l)                                                                               (ml) pH                                                                               Ua  Ub                                         __________________________________________________________________________     1 - E. coli TG1                                                                        -   W  CVA  15.5 1    5.2   0                                                  -   W  CVA  15.5 1    7.0   0                                                  -   W  AdN  15.5 1    5.2   0                                                  -   W  AdN  15.5 1    7.0   0                                          2 - E. coli TG1                                                                        +   W  CVA  1.4  1    4.0   28                                         pXL2087 +   W  CVA  1.4  1    5.2   27                                                 +   W  CVA  1.4  2    7.0   8                                                  +   S  CVA  1.4  1    5.2   25                                                 +   S  CVA  1.4  2    7.0   8                                                  +   W  AdN  0.3  1    4.2                                                                              159                                                    +   W  AdN  1.4  1    4.3   38                                                 +   W  AdN  1.4  2    6.2   18                                                 +   W  AdN  1.4  2    7.0   11                                                 +   S  AdN  1.4  2    6.2   17                                                 +   S  AdN  1.4  2    7.0   10                                         3 - E. coli TG1                                                                        -   W  CVA  1.2  2    4.0                                                                              --  10                                         pXL2087 -   W  CVA  1.2  2    5.2   14                                                 -   W  CVA  1.2  2    7.0   3.4                                                -   S  CVA  1.0  1    5.2   13                                                 -   S  CVA  1.0  1    7.0   3.2                                                -   W  AdN  0.3  1    4.2                                                                               75                                                    -   W  AdN  1.2  2    4.3   16                                                 -   W  AdN  1.2  2    6.2   11                                                 -   W  AdN  1.2  2    7.0   3.4                                                -   S  AdN  1.0  1    6.2   3                                                  -   S  AdN  1.0  1    7.0   4                                          4 - E. coli TG1                                                                        -   W  AdN  0.06 1    7.0                                                                               0  0                                          pXL2035                                                                        5 - E. coli TG1                                                                        -   W  AdN  0.24 1    7.0                                                                              270                                            pXL2158        CVA  1.25 1    7.0   8.3                                        6 - E. coli TG1                                                                        -   W  AdN  0.06 1    7.0                                                                              1500                                           pXL2035, 2158  CVA  0.2  1    7.0   70                                         7 - P. putida                                                                          -   W  AdN  0.3  1    7.0                                                                               0                                             G2081                                                                          pDSK519                                                                        8 - P. putida                                                                          -   W  CVA  0.25 1    7.0                                                                              130                                            G2081                                                                          pXL2169                                                                        __________________________________________________________________________      COMMON CONDITIONS: [substrate] = 50 mM; T = 25° C.; buffer 50 mM;       kinetics over 90 min for 1 to 3 and over 120 min for 4 to 8.                   ABBREVIATIONS: W = whole cells; S = sonicated cells; Ua = μmols of          cyanovalerate produced/h; Ub = μmols of adipate produced/h; AdN =           adiponitrile; CVA = 5cyanovalerate. DW = dry weight.                     

Example 7 Synthesis of Ammonium Adipate by the Batch Hydrolysis of Adiponitrile with E. coli (pXL2087) in Suspension

120 μl or 1068 μmol of adiponitrile were added at 25° C. and with magnetic stirring, at the reaction times 0, 1, 2, 3, 5, 6 and 7 h, to an initial volume of 5 ml of 50 mM phosphate buffer, pH 7, containing the strain E. coli (pXL2087) at an initial concentration of 21 g/l. The reaction was monitored analytically by taking 100 μl samples of the reaction volume every hour. The hydrolysis was found to proceed without a notable loss of kinetics.

The mean activities calculated over 30 min after addition of the adiponitrile are collated in Table 6 below.

                  TABLE 6                                                          ______________________________________                                         MEAN ACTIVITIES OF THE E. coli (pXL2087) CELLS                                 DURING THE HYDROLYSIS OF ADIPONITRILE                                                         SPECIFIC ACTIVITY                                               REACTION TIME (h)                                                                             μmol of adipate/h × mg of dry cells                    ______________________________________                                         0.5            16                                                              2.5            15                                                              5.5            11                                                              6.5            11                                                              7.7            15                                                              ______________________________________                                    

Example 8 Synthesis of Ammonium Adipate by the Hydrolysis of Adiponitrile in a Fixed Bed Reactor with E. coli (pXL2087) Immobilized on Resin

The E. coli (pXL2087) cells were first fixed by the technique described in U.S. Pat. No. 4,732,851.

The resulting biocatalyst was then used in a fixed bed column for the hydrolysis of adiponitrile to ammonium adipate.

8.1-Fixing of E. coli (pXL2087) to Resin

The cells were fixed according to the following protocol:

1 g (wet weight) of E. coli (pXL2087) with a solids content of 22%,

1 g of POLYCUP polyazetidine,

1 g of DUOLITE A 171 resin.

The gram of cells was suspended in the polyazetidine solution. After homogenization, the resin was poured into the cell suspension. The whole was stirred with a spatula and then left to dry for 18 h, open to the air, under a hood. 4 ml or 1.3 g of biocatalyst were thus collected. The activities of the immobilized and free cells were determined at 25° C. and pH 7 on a 50 mM solution of adiponitrile. They are respectively 30 and 110 μmol of 2-cyanovalerate/h/mg of cells DW, from which a fixing yield of 26% is deduced.

8.2-Hydrolysis of Adiponitrile in a Fixed Bed Reactor

The half-life is determined in a continuously fed fixed bed reactor under the conditions indicated below:

T 28° C.; catalyst 0.5 g or 2 ml or 85 mg of cells (dry weight); [adiponitrile] 50 mM; phosphate buffer 50 mM, pH 7; flow rate 3.7+/-0.1 ml/h; column: diameter 1 cm, height 3 cm.

The initial activity of the cells was 1.5 μmol of adipate/h/mg of cells (dry weight). 66% of the initial activity is preserved after 32 days or 770 h.

Example 9 Synthesis of Ammonium Methioninate by Hydrolysis of Methiononitrile, with Recombinant Strains in Suspension

The recombinant strains used in this example are those from E. coli TG1, integrating the plasmids PXL2158 and PXL2035 described above and containing the nitrilase gene of Comamonas testosteroni.

Tests 9 to 13 show the nitrilase activity at 28° C., of these recombinant strains with respect to the methiononitrile, according to various operating conditions. The strain culture is performed as explained in example 6.1. The following Table 7 summarizes the conditions and the results of tests 9 to 13.

                  TABLE 7                                                          ______________________________________                                                      OPERATING         Initial                                                      CONDITIONS        specific                                        MICRO-                        Vol-     activity                                ORGANISM     Substrate                                                                               [DW]    ume      μmol/h ×                       Nature    State  (mM)     (g/l) (ml) pH  mg of DW                              ______________________________________                                         9 - E. coli                                                                              W      MetCN    17.2  5    7    8                                    PXL2158          (100)                                                         10 - E. coli                                                                             W      MetCN    1.4   5    7   77                                    PXL2158 +         (50)                                                         2035                                                                           11 - E. coli                                                                             W      MetCN    1.4   5    7   62                                    PXL2158 +         (50)                                                         2035                                                                           12 - E. coli                                                                             W      MetCN    1.4   5    7   73                                    PXL2158 +        (100)                                                         2035                                                                           13 - E. coli                                                                             W      MetCN    1.4   5    7   61                                    PXL2158 +        (200)                                                         2035                                                                           ______________________________________                                          ABBREVIATIONS: W = whole cells; DW = dry weight of cells; MetCN =              methiononitrile.                                                               COMMENTS ON TABLE 7: Tests 9 and 10 show that the recombinant strain E.        coli PXL2158 possesses a good nitrilase activity but that it is                recombinant strain E. coli combining PXL2158 and PXL2035, which is the         most interesting strain as regards performances, thanks to an activity         which is almost 10 times greater; about 80 μmol of MEtCN/h × mg       of DW. Tests 11 to 13 show that the initial quantity of MetCN substrate        has only a small influence on the activities obtained.                   

Example 10 Synthesis of Ammonium Methioninate by Hydrolysis of Methiononitrile, with E. coli PXL 2158+2035 Cells Fixed on Resin

The E. coli PXL 2158+2035 free cells are fixed on resin according to the technique described in U.S. Pat. No. 4,732,851, so as to form a biocatalyst.

10.1-Fixing Yield and Activity of the Biocatalyst

The results of the initial activities of the biocatalyst and of the free cells are given in Table 8 below.

                  TABLE 8                                                          ______________________________________                                         SPECIFIC INITIAL ACTIVITES OF HYDROLYSIS OF                                    THE METHIONONITRILE OF THE FREE AND FIXED                                      CELLS OF E. coli PXL 2158 + 2035                                               Dry                     Specific Initial Activity                                      biocatalyst                                                                              Dry cells μmol/h ×                                                                      μmol/                                   TEST No.                                                                               g/l       g/l       mg DB   h × mg DC                            ______________________________________                                         14      10.3      1.4       3       22                                         15      --        1.3       --      63                                         ______________________________________                                         CONDITIONS: volume = 5 ml; potassium phosphate buffer =                        100 mM pH7, [MetCN] = 50 mM; T 28° C.; kinetics over 3 h;               DB = dry biocatalyst; DC = dry cells.                                          COMMENTS: the activity of the biocatalyst is 3 μmol/h × mg of         dry biocatalyst at 28° C. and the fixing yield is 35%.                  With the free or fixed cells, 5% to 6% of amides are produced at               the end of the hydrolysis.                                                

10.2-Influence of the Initial Methiononitrile Concentration

Two methiononitrile batches were tested: purified methiononitrile in the form of a sulfate and free methiononitrile. The results are summarized in Table 9 below.

                  TABLE 9                                                          ______________________________________                                         INFLUENCE OF THE INITIAL METHIONONITRILE                                       CONCENTRATION ON THE SPECIFIC INITIAL                                          ACTIVITY OF E. coli PXL 2158 + 2035                                                              Specific initial                                                               activity                                                     [MetCN]                 μmol/                                                                               μmol/                                                                             Amide                                                          Dry     h ×                                                                            h ×                                                                            formed *                             TEST  sulfate Free    biocatalyst                                                                            mg    mg    formed *                             No.   mM      mM      g/l     DB    DC    %                                    ______________________________________                                         16     50     --      10.3    3.0   22.0  5.9                                  17    100     --      10.0    3.4   25.1  6.0                                  18    200     --      10.5    4.2   30.5  8.3                                  19    300     --      10.2    4.2   30.5  10.6                                 20    --      105     9.9     2.7   20.0  9.6                                  21    --      210     10.0    2.9   20.8  12                                   22    --      315     9.7     2.4   17.7  16                                   ______________________________________                                          CONDITIONS: volume = 5 ml; potassium phosphate buffer = 100 mM pH7; T          28° C.; kinetics over 3 h; * = percent with respect to the formed       acid; DB = dry biocatalyst; DC = dry cells.                                    COMMENTS: the specific initial activity slightly increases up to 200 mM o      methiononitrile. The percent of formed amide increases with the initial        nitrile concentration. The purified methiononitrile makes it possible to       obtain a better activity and a low percent of amide.                     

    __________________________________________________________________________     SEQUENCE LISTING                                                               (1) GENERAL INFORMATION:                                                       (iii) NUMBER OF SEQUENCES: 5                                                   (2) INFORMATION FOR SEQ ID NO:1:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 27 amino acids                                                     (B) TYPE: amino acid                                                           (C) STRANDEDNESS: Not Relevant                                                 (D) TOPOLOGY: Not Relevant                                                     (ii) MOLECULE TYPE: peptide                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                        MetLysAsnTyrProThrValLysValAlaAlaValGlnAlaAlaVal                               151015                                                                         PheMetAsnLeuGluAlaThrValAspLysThr                                              2025                                                                           (2) INFORMATION FOR SEQ ID NO:2:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 9 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: Not Relevant                                                 (D) TOPOLOGY: Not Relevant                                                     (ii) MOLECULE TYPE: peptide                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                        MetLysAsnTyrProThrValLysVal                                                    15                                                                             (2) INFORMATION FOR SEQ ID NO:3:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 26 base pairs                                                      (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: unknown                                                      (D) TOPOLOGY: unknown                                                          (ii) MOLECULE TYPE: DNA (genomic)                                              (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                        ATGAAGAATTATCCNACNGTCAAGGT26                                                   (2) INFORMATION FOR SEQ ID NO:4:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1194 base pairs                                                    (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: unknown                                                      (D) TOPOLOGY: unknown                                                          (ii) MOLECULE TYPE: DNA (genomic)                                              (ix) FEATURE:                                                                  (A) NAME/KEY: CDS                                                              (B) LOCATION: 87..1148                                                         (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                        CTCGAGACAAAATTGGGACAGTCGCCCCCTATCTGCAAAATGGAACCTCCTTTGCACATC60                 TATAAAATTTTTTGAGGAAGACAGCAATGAAAAATTATCCTACAGTCAAGGTA113                       MetLysAsnTyrProThrValLysVal                                                    15                                                                             GCAGCAGTGCAAGCTGCTCCTGTATTTATGAATCTAGAGGCAACAGTA161                            AlaAlaValGlnAlaAlaProValPheMetAsnLeuGluAlaThrVal                               10152025                                                                       GATAAAACTTGTAAGTTAATAGCAGAAGCAGCATCTATGGGCGCCAAG209                            AspLysThrCysLysLeuIleAlaGluAlaAlaSerMetGlyAlaLys                               303540                                                                         GTTATCGGCTTCCCAGAAGCATTTATTCCCGGCTATCCATATTGGATT257                            ValIleGlyPheProGluAlaPheIleProGlyTyrProTyrTrpIle                               455055                                                                         TGGACATCAAATATGGACTTCACTGGAATGATGTGGGCCGTCCTTTTC305                            TrpThrSerAsnMetAspPheThrGlyMetMetTrpAlaValLeuPhe                               606570                                                                         AAGAATGCGATTGAAATCCCAAGCAAAGAAGTTCAACAAATTAGTGAT353                            LysAsnAlaIleGluIleProSerLysGluValGlnGlnIleSerAsp                               758085                                                                         GCTGCAAAAAAGAATGGAGTTTACGTTTGCGTTTCTGTATCAGAGAAA401                            AlaAlaLysLysAsnGlyValTyrValCysValSerValSerGluLys                               9095100105                                                                     GATAATGCCTCGCTATATTTGACGCAATTGTGGTTTGACCCGAATGGT449                            AspAsnAlaSerLeuTyrLeuThrGlnLeuTrpPheAspProAsnGly                               110115120                                                                      AATTTGATTGGCAAGCACAGGAAATTCAAGCCCACTAGTAGTGAAAGA497                            AsnLeuIleGlyLysHisArgLysPheLysProThrSerSerGluArg                               125130135                                                                      GCTGTATGGGGAGATGGGGATGGAAGCATGGCTCCCGTATTTAAAACA545                            AlaValTrpGlyAspGlyAspGlySerMetAlaProValPheLysThr                               140145150                                                                      GAGTATGGGAATCTTGGGGGACTCCAGTGCTGGGAACATGCTCTCCCA593                            GluTyrGlyAsnLeuGlyGlyLeuGlnCysTrpGluHisAlaLeuPro                               155160165                                                                      TTAAACATTGCGGCGATGGGCTCATTGAACGAACAGGTACATGTTGCT641                            LeuAsnIleAlaAlaMetGlySerLeuAsnGluGlnValHisValAla                               170175180185                                                                   TCCTGGCCAGCCTTCGTCCCTAAAGGCGCAGTATCATCCAGAGTATCA689                            SerTrpProAlaPheValProLysGlyAlaValSerSerArgValSer                               190195200                                                                      TCCAGCGTCTGTGCGTCTACTAATGCGATGCATCAGATCATTAGTCAG737                            SerSerValCysAlaSerThrAsnAlaMetHisGlnIleIleSerGln                               205210215                                                                      TTTTACGCGATCAGCAATCAGGTATATGTAATTATGTCAACCAATCTC785                            PheTyrAlaIleSerAsnGlnValTyrValIleMetSerThrAsnLeu                               220225230                                                                      GTTGGCCAAGACATGATTGACATGATTGGGAAAGATGAATTTTCCAAA833                            ValGlyGlnAspMetIleAspMetIleGlyLysAspGluPheSerLys                               235240245                                                                      AACTTTCTACCGCTTGGTTCTGGAAACACAGCGATTATTTCTAACACC881                            AsnPheLeuProLeuGlySerGlyAsnThrAlaIleIleSerAsnThr                               250255260265                                                                   GGTGAGATTTTGGCATCAATTCCACAAGACGCGGAGGGAATTGCTGTT929                            GlyGluIleLeuAlaSerIleProGlnAspAlaGluGlyIleAlaVal                               270275280                                                                      GCAGAGATTGACCTTAACCAAATAATTTATGGAAAGTGGTTACTGGAT977                            AlaGluIleAspLeuAsnGlnIleIleTyrGlyLysTrpLeuLeuAsp                               285290295                                                                      CCCGCCGGTCATTACTCTACTCCCGGCTTCTTAAGTTTGACATTTGAT1025                           ProAlaGlyHisTyrSerThrProGlyPheLeuSerLeuThrPheAsp                               300305310                                                                      CAGTCTGAACATGTACCCGTAAAAAAAATAGGTGAGCAGACAAACCAT1073                           GlnSerGluHisValProValLysLysIleGlyGluGlnThrAsnHis                               315320325                                                                      TTCATCTCTTATGAAGACTTACATGAAGATAAAATGGATATGCTAACG1121                           PheIleSerTyrGluAspLeuHisGluAspLysMetAspMetLeuThr                               330335340345                                                                   ATTCCGCCGAGGCGCGTAGCCACAGCGTGATCGCCGCCTCTCGGGGC1168                            IleProProArgArgValAlaThrAla                                                    350                                                                            GTTCGGTTGCTGATAGCCATCGCCTT1194                                                 (2) INFORMATION FOR SEQ ID NO:5:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 354 amino acids                                                    (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:                                        MetLysAsnTyrProThrValLysValAlaAlaValGlnAlaAlaPro                               151015                                                                         ValPheMetAsnLeuGluAlaThrValAspLysThrCysLysLeuIle                               202530                                                                         AlaGluAlaAlaSerMetGlyAlaLysValIleGlyPheProGluAla                               354045                                                                         PheIleProGlyTyrProTyrTrpIleTrpThrSerAsnMetAspPhe                               505560                                                                         ThrGlyMetMetTrpAlaValLeuPheLysAsnAlaIleGluIlePro                               65707580                                                                       SerLysGluValGlnGlnIleSerAspAlaAlaLysLysAsnGlyVal                               859095                                                                         TyrValCysValSerValSerGluLysAspAsnAlaSerLeuTyrLeu                               100105110                                                                      ThrGlnLeuTrpPheAspProAsnGlyAsnLeuIleGlyLysHisArg                               115120125                                                                      LysPheLysProThrSerSerGluArgAlaValTrpGlyAspGlyAsp                               130135140                                                                      GlySerMetAlaProValPheLysThrGluTyrGlyAsnLeuGlyGly                               145150155160                                                                   LeuGlnCysTrpGluHisAlaLeuProLeuAsnIleAlaAlaMetGly                               165170175                                                                      SerLeuAsnGluGlnValHisValAlaSerTrpProAlaPheValPro                               180185190                                                                      LysGlyAlaValSerSerArgValSerSerSerValCysAlaSerThr                               195200205                                                                      AsnAlaMetHisGlnIleIleSerGlnPheTyrAlaIleSerAsnGln                               210215220                                                                      ValTyrValIleMetSerThrAsnLeuValGlyGlnAspMetIleAsp                               225230235240                                                                   MetIleGlyLysAspGluPheSerLysAsnPheLeuProLeuGlySer                               245250255                                                                      GlyAsnThrAlaIleIleSerAsnThrGlyGluIleLeuAlaSerIle                               260265270                                                                      ProGlnAspAlaGluGlyIleAlaValAlaGluIleAspLeuAsnGln                               275280285                                                                      IleIleTyrGlyLysTrpLeuLeuAspProAlaGlyHisTyrSerThr                               290295300                                                                      ProGlyPheLeuSerLeuThrPheAspGlnSerGluHisValProVal                               305310315320                                                                   LysLysIleGlyGluGlnThrAsnHisPheIleSerTyrGluAspLeu                               325330335                                                                      HisGluAspLysMetAspMetLeuThrIleProProArgArgValAla                               340345350                                                                      ThrAla                                                                         __________________________________________________________________________ 

We claim:
 1. Polypeptides having nitrilase activity and resulting from the expression of a DNA segment selected from the group consisting of:1) the DNA sequence shown in SEQ ID No. 4; 2) a degenerate of said DNA sequence resulting from the degeneracy of the genetic code; and, 3) a DNA molecule that hybridizes with the complement of said DNA sequence or analog thereof under the following conditions:a) hybridization buffer: 5×SSC, 5×Denhardt, 0.1% SDS, 50 mM Na₃ PO₄, pH 6.5, 250 μg/ml of ssDNA; b) hybridization temperature: 50° C.; and, c) washing conditions: 1 h, 6×SSC, room temperature, and 5 min, 2×SSC, 0.1% SDS, 50° C.; and wherein said DNA molecule encodes a polypeptide having nitrilase activity.
 2. Enzymatic method of converting nitriles, characterized in that it consists in bringing the nitriles into contact with a polypeptide having a nitrilase activity, according to claim
 1. 3. Method according to claim 2, characterized in that the nitrile is a dinitrile of the formula NC--R--CN in which R is an alkylene group having from 1 to 10 carbon atoms.
 4. Method according to claim 2, characterized in that the nitrile is adiponitrile.
 5. Method according to claim 2, characterized in that the nitrile is a mononitrile.
 6. Method according to claim 5, characterized in that the nitrile is the methiononitrile.
 7. The method of claim 5 wherein the mononitrile belongs to the class of aliphatic sulphurized mononitriles.
 8. Polypeptide according to claim 1, characterized in that it comprises the sequence designated by SEQ ID NO: 5 in the enclosed sequence listing and given hereinunder ##STR6##
 9. Enzymatic method of converting nitriles, characterized in that it consists in bringing the nitriles into contact with a polypeptide having a nitrilase activity, according to claim
 8. 10. Method according to claim 9, characterized in that the nitrile is a dinitrile of the formula NC--R--CN in which R is an alkylene group having from 1 to 10 carbon atoms.
 11. Method according to claim 10, characterized in that the nitrile is adiponitrile.
 12. Method according to claim 10, characterized in that the nitrile is a mononitrile.
 13. Method according to claim 12, characterized in that the nitrile is methiononitrile.
 14. The method of claim 12 wherein the mononitrile belongs to the class of aliphatic sulphurized mononitriles. 